A system log is a file that records either the events which happen while an operating system or other software runs, or the personal messages between different users of a communication software or a multiplayer game. The act of keeping a log file is called logging. In the simplest case, log messages are written to a single log file. Additionally, an event log record events taking place in the execution of a system in order to provide an audit trail that can be used to understand the activity of the system and to diagnose problems. Event logs aid administrators to understand the activities of complex systems, particularly in the case of applications with little user interaction (such as server applications). System logs can be used for computer system management and security auditing as well as generalized informational, analysis, and debugging messages.
System administrators have a dilemma as to setting the proper level of system logging. For instance, outputting too few messages prevents using diagnostic software to determine the causes of errors. Conversely, having an application constantly storing too many messages will put unnecessary load on storage, CPU, and network resources, potentially harming the performance and availability of the system.